1. Field of the Invention
The present invention relates to a semiconductor device. In particular, it relates to a semiconductor device on which a plurality of semiconductor elements are mounted as being stacked on one another in the thickness direction thereof.
2. Description of the Related Art
A semiconductor device with a lead frame, in general, includes an island and a plurality of leads each of which has a first end disposed near the island. To the top surface of the island, a semiconductor element is fixed, and thin metallic wires are provided to connect the leads with the bonding pads of the semiconductor elements (see, for example, Japanese Patent Application Publication No. 2007-5569). In addition, the island, the leads, the semiconductor element, and the thin metallic wires are encapsulated using an insulating resin while second end portions of the leads are left exposed. In each of the leads, the part encapsulated by the insulating resin is termed as an inner lead while the part exposed out of the insulating resin is termed as an outer lead. The outer lead is folded when necessary, and thus a second end of the lead is bonded to a printed circuit board or the like by a method, such as soldering.
Incidentally, a stack-type semiconductor device has been developed with a plurality of chips being stacked on an island. In this type of device, a child chip with a smaller size than a parent chip is stacked on the parent chip, and the parent and the child chips are electrically connected with each other with thin metallic wires.
Semiconductor devices with such a structure as described above benefit from the recent development of techniques for making anything lighter in weight, thinner in thickness, shorter in length, and smaller in dimension. In other words, miniaturization of such semiconductor devices is now made possible. Nevertheless, the semiconductor devices of the type still have their own problems. The top surface of the child chip is located at a higher position than the top surface of the parent chip on the island, that is, the top surface of the child chip is farther away from the surface of the island than the top surface of the parent chip is. When a thin metallic wire is connected with the top surface of the child chip, the highest portion of the thin metallic wire reaches an even higher position. As a result, the semiconductor device, precisely the package, is made thicker.